MOSCOW -- Russian billionaire Viktor Vekselberg has stepped down as chairman of aluminum giant Rusal and warned of a "deep crisis" at the commodities behemoth.

Vekselberg's statement of resignation prompted Rusal, the world's largest aluminum producer, to suspend trading of its shares after they shed 1.3 percent of their value on the Hong Kong Stock Exchange.

Vekselberg wrote in a statement issued late on March 12 that Rusal was being badly managed and had been weighed down by debt.

Rusal's shares have fallen more than 40 percent since its January 2010 listing.

Company officials say Vekselberg failed to fulfill his duties as board chairman over the past year and had to be replaced.